The tantalum stopped-flow microcalorimeter has been utilized this year in the initiating of studies of isoionic binding studies, both of ligand and effector molecules, and for the study of the study of the binding of endotoxin (lipid polysaccharide to hemoglobin. Various improvements in the ease of operation of the calorimeter and to its versatility have been initiated as a result of suggestions from several researchers using the instrument. The new pulsed heat capacity calorimeter has been improved considerably and the mathematics worked out for the simultaneous measurement of both the heat capacity and thermal conduction of a liquid sample.